The horizontal type continuous casting machine has recently been industrialized for the urpose of manufacturing cast steel strands. In this machine, a cast steel strand is horizontally and intermittently withdrawn from a horizontal mold fitted to a lower portion of a side wall of a tundish with molten steel received therein by means of a plurality of cycles each comprising one pull, one pause and one push. More particularly, the cast steel strand is first pulled from the horizontal mold in the horizontal direction at a prescribed pulling speed for a prescribed pulling period of time, then the pulling of the cast steel strand is paused for a prescribed pausing period of time, and then the cast steel strand is pushed back in the direction opposite to the pulling direction for a prescribed pushing period of time. This push prevents the solidified shell of the cast steel strand from being broken in the horizontal mold under the effect of thermal contraction, which otherwise results in breakout.
Pulling of the cast steel strand is paused for the prescribed pausing period of time as described above for the purpose of increasing the thickness of the solidified shell of the cast steel strand in the horizontal mold prior to pushing back of the cast steel strand in the direction opposite to the pulling direction, and thus preventing the solidified shell from buckling during pushing back of the cast steel strand.
A conventional apparatus for horizontally and intermittently withdrawing a cast steel strand in the manner as described above from a horizontal mold of a horizontal type continuous casting machine comprises at least one pair of pinch rolls and a driving device. The at least one pair of pinch rolls horizontally and intermittently withdraws the cast steel strand from the horizontal mold by means of a plurality of cycles each comprising one pull for a prescribed period of time, one pause for a prescribed period of time and one push for a prescribed period of time, and the driving device drives the at least one pair of pinch rolls through a driving force transmitting means in response to the abovementioned one pull, one pause and one push in each cycle.
However, when the weight per unit length of the cast steel strand increases, the driving device does not stop at once but overshoots the prescribed limit even upon receiving an instruction signal to stop the pull of the cast steel strand, under the effect of inertia of the cast steel strand acting on the driving device. Consequently, the cast steel strand is pulled from the horizontal mold over the prescribed pulling period of time, causing not only deterioration of quality of the cast steel strand but also increasing risk of breakout.
During the push of the cast steel strand, since the cast steel strand is pushed back only slightly, the driving device never overshoots the prescribed limit under the effect of inertia of the cast steel strand as in the pull of the cast steel strand.
Under such circumstances, there is a demand for the development of an apparatus which permits an accurate pulling of a cast steel strand, which is manufactured by a horizontal type continuous casting machine, from a horizontal mold thereof without exceeding a prescribed pulling period of time even when the weight per unit length of the cast steel strand increases, but such an apparatus has not as yet been proposed.